> Get paying customers first, you can still incorporate a GmbH later. On the other hand: If nobody pays you money, you don't need a GmbH or be a sole proprietor.
is it possible to sell the product first and then register as Einzelunternehmer later (within the same fiscal year)? Or you have to register before?
After registering as Einzelunternehmer, if the business stops existing, does one have to "close activity" as Einzelunternehmer somehow?
You can only do some occasional work without registering yourself in any special form.
You can check, if you can start as a Freiberufler. It is a bit more lightweight than going with Einzelunternehmen. For example, I am a Freiberufler now working as a consultant / contractor in data engineering and management. I can also potentially sell my product, but I did not check the limitations.
You do not have to close you Einzelunternehmen afaik, if you do not make money, but you are still responsible for sending regular declarations to the Finanzamt.
is it possible to sell the product first and then register as Einzelunternehmer later (within the same fiscal year)? Or you have to register before?
After registering as Einzelunternehmer, if the business stops existing, does one have to "close activity" as Einzelunternehmer somehow?